Electrical control system



April 9, 1929. 5 ox 1,708,384

ELECTRICAL CONTROL SYSTEM Filed Jan. 20, 1925 INVENTOR. /7/o/J /0X ATTORNEY Patented Apr. 9, 1 929.

UNITED STATES PATENT OFFICE.

HAROLD E. FOX, 0]? PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO CENTRAL ELECTRIC TOOL COMPANY, A CORPORATION OF PENNSYLVANIA.

ELECTRICAL CONTROL SY STEM.

Application filed January 20, 1925. Serial No. 3,696.

This invention relates to electrical control systems and is particularly adaptable to systems for controlling sign flashing and for controlling the operation of 'hoist or elevator motors, or circuits, or devices to be periodically energized.

The-object of this invention is to provide a novel method of and means for opening an alternating current circuit without drawing an arc.

Another object of my invention is to provide a control system which shall be relatively simple, reliable and economical.

In practicing my invention, provide two unilateral current conducting devices, preferably electronic tubes, and two relays, one in series with each tube, between the alternating current supply circuit and the load circuit. The two circuits, each including an electronic valve and a relay, are connected in inverted parallel relation, that is, one tube is connected in such manner as to transmit the positive current impulses and the other tube to transmit the negative current impulses. Each of the circuits includes a switching element of the relay, which is held closed while the relay is energized but which opens when the current traversing the tube and the relay decreases to zero, unless the relay switch is otherwise held closed.

. Each relay is provided with an operating winding which may be periodically energized as by a motor driven switch for flashing, or by an elevator operating switch, or other equivalent means. When the operating windings are so energized, the relays.

connect the electronic valve between the supply circuit and the load circuit to transmit current therebetween. When it is desired to disconnect the load circuit and the switch is opened, the operating coils of the relays are de-energized but the holding coils which are in series with the electronic valves remain energized until the current through the associated valve decreases to zero. The relay switches thereupon open to disconnect the associated valves from the load circuit.

Since each valve is so connected as to transmit impulses of only one polarity, no current will traverse the respective valves for the duration of the intervals between such impulses. connected to transmit the positive current impulses and the other to transmit negative current impulses, the sine wave alternating Inasmuch as one valve iscurrent will be transmitted to the load circuit so long as both relay switches are closed;

relay switch will open. The two switches should open within practically one cycle after the main operating switch has been opened. Inasmuch as the relay switches open when there is no current traversing the electron valves and, consequently, the relay switches, there will be no arcing when the load circuit is disconnected from the supply circuit.

In Fig. 1 of the accompanying drawings, is a diagrammatic view of an electrical circuit containing apparatus arranged to operate in accordance with the foregoing deseription;

Fig. 2 is a schematic view of the system illustrated in Fig. 1, illustrating a motoroperated switch for sign flashing or similar Work;

Fig. 3 is a diagrammatic view of an elevator motor system operating in accordance with the principle of the system illustrated in Fig. l; and

Fig. 4c is a graphic view of the current wave impulses transmitted by the respective electric valves.

As illustrated in Figs. 1 and 2, alternating current energy is derived from a generator or alternating current supply circuit 1 and supplied to a load circuit 2 containing elec-. tric lamps 3 or inductive load 1. Two electric valves 5 and 6 of the electronic type and two relays 7 and 8 are provided to connect the load circuit 2 and the connected load to the supply circuit 1, when such connection is desired, in response to the closure of the switch 9, which maybe manually operated as in Fig. 1, or switch 25 motor operated as illustrated in Fig. 2.

The "alves 5 and 6 in the example illustrated are of the electronic type, comprising an electron-emitting filament f and an anode or plate a in a closed vessel. Energy for the filaments of both valves is derived from the circuit 1 through a transformer 11, the primary winding of which is controlled by a relay switch 12 in response to the operation of the main switch 9. The relay 7 embodies a switch element 13, an operating coil 1% and a holding coil 15. Similarly, the relay 8 embodies a switch 16, an operating coil 17 and a holding coil 18.

The filament of the valve 5 and the plate of the valve 6 are connected to conductor 20 of the supply circuit 1. The plate of valve 5 is connected in circuit with the holding coil and the switch element 13 of the relay 7. Similarly, the filament of the valve 6 is connected in circuit with the holding coil 18 and the switch element 16 of relay 8. The switch elements 13 and 16 of the relay 7 and 8 are joined and connected to the load circuit 2 by a conductor 21. The operating coils 1d and 17 of the two relays 7 and 8 are connected in series with the winding of relay 12 and the main switch 9 across the supply circuit 1. Thus, when the switch 9 is closed, the relay 12 closes to energize the filaments of the electronic valves 5 and 6, and to operate the relays 7 and 8 to close the associated switches 13 and 16. The circuit 2 is then connected to the circuit 1 through the switches 7 and 8 and the valves 5 and 6.

When the conductor is negative with respect to the other conductor 22 of the supply circuit 1, the filament of valve 5 1S negative with respect to its plate, and current will therefore be transmitted by the valve 5 from the supply circuit 1 to the load circuit 2. At the same time, however, the plate of valve 6 will be negative with respect to its filament, and the valve 6 will therefore be non-conductive and will not transmit current between the supply and load circuits. As the polarity of the circuit changes, however, and the conductor 20 becomes positive, the valve 5 becomes nonconductive since its filament is now positive with respect to its plate. At the same time, however, the valve 6 becomes conductive since the plate is positive with respect to the filament which is the condition conductive to current conduction.

Thus, upon closure of the switch 9, the filaments of the valves are energized and the relays 7 and 8 are operated to connect the valves 5 and 6 between the supply and load circuits, and current is transmitted therebetween. As soon as the switch 9 is opened, the operating coils 14: and 17 are de-energized. So long as current traverses the windings 15 and 18, however, their switches will remain closed. Inasmuch as the valve 5 will transmit only impulses of one polarity and the valve 6 only impulses of opposite polarity, there will be intervals between such impulses when no current will be transmitted, as illustrated in Fig. 4, in. which V is the electromotive-force and 5 and 6 are the current impulses through the valves 5 and 6. Consequently, the associated holding windings 15 and 18 will be de-enermeasea gized during such intervals and the relays 7 and 8 will assume their normal de-encrgized positions. The valves 5 and 6 will thus be disconnected from the load circuit and no current will be transmitted to the load circuit from the supply circuit 1.

Tnasmlu ch as the relay switches 13 and 16 open wlun no current is traversing the circuit in which they are disposed, there is no arcing to attend such opening and, consequently, there is nothing to cause deterioration of the switch contacts.

In Fig. 1, T have illustrated the switch 9 as being a manually operable switch. In Fig. 2, ll have illustrated a motor-operated switch in which the switching operations are controlled by a contact on a drum which is controlled by a motor 26 that is energized from the supply circuit 1. The timing device 27 is shown schematically. It may be of any of the well known commercial time switches which close at a predetermined time and remain closed for a definite interval, as, for example, during the evening hours when the operation of the sign flashing device may be desired.

In Fig. 3, T have illustrated a circuit for controlling the operation of a hoist or elevator motor. Energy is derived from a polyphase alternating current generator or supply circuit 30 and is supplied to a hoist or elevator motor 31 through a starting and reversing apparatus 32 and non-arcing units 35, 36 and 37, each of which is disposed in a conductor between the generator or supply circuit and the motor. The starting and reversing apparatus is illustrated for simplicity merely by a rectangle since the operation and construction of such apparatus is well known and need not be described in detail other than to specify the function thereof.

The several non-arcing units 35, 36 and 37 are similar to the units illustrated and described in Figs. 1 and 2. The operation of the starting and reversing apparatus 32 and the connection of the non-arcing units thereby, between the generator and the motor, are controlled by a switch 38 which is disposed on the elevator and is subject to control of the operator. The switch 38 comprises a movable member 39 which ongages contacts 40 and 41 when moved to the left hand side, and contacts 42 and 43 when moved to the right hand side. The switch 38 is adapted when operated in one direction to complete a circuit including all of the operating coils of the relays associated with the valves of the non-arcing units, thereby closing the switches and connecting the circuits of the valves between the generator and the motor. At the same time a circuit is completed that controls the operation of the starting and reversing switching apparatus which connects the generator iii iii

by gradual voltage or currentsteps to the motor, to permit the motor to accelerate in response to gradually increased energization. When-operation of the motor is no longer desired, the switch 39 is opened, and the non-arcing units respectively open the associated relay switches to disconnect the associated conductors until the motor is discdnnected from the generator.

When operation of the motor is desired in av reversed direct-ion, the switch 39 is operated to the opposite side. The nonarcing units are again connected in circuit between the generator and motor, and the starting and the reversing apparatus 32 is properly operated to connect the motor to the generator to cause the motor to rotate in a reversed direction. lVhen the operation of the motor is again no longer desired, the main switch is opened by the operator and the non-arcing units again operate to open their respective circuits when no current traverses the valves.

By means of a system of the foregoing character in which the circuits are opened when no current traverses the circuit for an interval of extended duration, all arcing is obviated and excessive wear due to burning and pitting of contact surfaces is eliminated.

My invention is not limited to the specific devices that are illustrated, nor to the arrangement that is shown, but may l e mod1- fied without departing from the spir t and scope of the invention as set forth in the appended claims.

I claim as my invention:

1. The combination with a source of alternating current, of an electric valve and a switch in series with each other in the circuit of said source for transmitting the load current thereof, means energized by the load current transmitted through said valve and switch for holding said switch closed until the current through said valve falls to substantially zero magnitude and means thereupon effecting opening of said switch. 2. The combination with a source of altcrnating current, of an electric valve and a switch biased toward open position in series with each other in the circuit of said source for transmitting the load current thereof, means energized by the load current transmitted through said valve and switch for holding said switch closed until the current through said valve falls to substantially zero magnitude and means thereupon effecting opening of said switch.

3. The combination with a source of alternating current, of an electric valve and a switch in series with each other in the circuit of said source for transmitting the load current thereof, an operating coil for moving said switch to closed position, a holding coil traversed by load current transmitted through said valve for holding said switch in closed position after.deenergization of said operating coil until t-hecin'rent through said valve. falls to substantially zero magnituda and means thereupon effecting opening of said switch.

4. The eon'ibination with a source of alternating current, of an electric valve continuingly asymmetrically conductive, a switch in series with said valve in the circuit of said source andthrough which and said valve the load current of said source is transmitted, and means responsive to the fall of current in said valve to substantially zero magnitude causing said switch to open.

5. The combination with a source of alternating current, of an electric valve and a switch in series with each other in the circuit of said source for transmitting the load current thereof, an operating coil for moving and holding said switch to and in closed position, a holding coil energized by the load current traversing said valve for holding the switch closed after deenergization of the operating coil until the current through said valve falls substantially to zero magnitude and means thereupon effecting opening of said switch.

6. The combination with a source of alternating current, of an electric valve and a switch in series with each other in the cir cuit of said source for transmitting the load current thereof, an operating coil for moving said switch to closed position, a holding coil traversed by load current transmitted through said valve for holding said switch in closed position after deenergization of said operating coil until the current through said valve falls to substantially zero magnitude, means for maintaining said valve conductive, and switching mechanism for controlling simultaneous energization of said means and of said operating coil.

7. The combination with a source of alternating current, of a thermionic valve and a switch in series with each other in the circuit of said source and through which the load current of said source is transmitted, means controlled by the current transmitted through said valve for holding said switch closed until the current through said valve falls substantially to zero magnitude and means thereupon effecting opening of said switch. Y

8. The combination with a source of alternating current, of a thermionic valve and a switch in series with each other in the circuit of said source and through which the load current of said source is transmitted, means controlled by the current transmitted through said valve for holding said switch closed until the current through said valve falls substantially to zero magnitude and. means thereupon eflecting opening of said switch, an operating coil for moving said switch to closed position, and switching lncchanisni controlling the simultaneous en ergization of the cathode of said valve and of said operating coil.

9. The combination with a source of alternating current, of a pair of electric valves connected in inverted parallel relation with each other, a switch in series with each of said valves said valves and switches transmitting the load current of said source, norlnall energized electro-magnetic means holding said switches closed while said load current is flowing, electro-1nagnetic means controlled by the valve current for llOldlllg said switches closed after deenergization of said first named electro-magnetic means until the valve current falls substantially to zero magnitude and means thereupon efi'ecting opening of said switch.

In testimony whereof, I have hereunto subscribed my name this l9th day of J anu- 20 HAROLD E. FOX. 

